In general, silicon wafers are fabricated through a process for growing a silicon single crystalline ingot, a process for slicing the ingot into disc-type wafers and a process for polishing the wafer surface, and the resultant silicon wafers are provided to manufacture semiconductor devices. However, in the process for growing a silicon single crystalline ingot, crystal defects caused by crystal growing and undesired impurities that are not caused by crystal growing may be included in a silicon single crystalline ingot and a wafer. Such crystal defects or impurities cause faults to a semiconductor device, and thus they should be removed.
FIG. 1 is a view showing crystal defects reported so far. In FIG. 1, small circles are silicon atoms.
As shown in FIG. 1, various types of crystal defects may be included in a silicon single crystalline ingot or a wafer, and the crystal defects may be classified into a point defect, a line defect, a plane defect and a volume defect according to how they exist in a crystal.
The point defect may include an intrinsic point defect and an extrinsic point defect. The intrinsic point defect includes a vacancy ((a) in FIG. 1) and a self-interstitial atom ((b) in FIG. 1). The extrinsic point defect includes a substitutional impurity atom ((c) in FIG. 1), an interstitial impurity atom ((d) in FIG. 1) and a dangling bond ((e) in FIG. 1). The line defect includes an edge dislocation ((f) in FIG. 1) and a screw dislocation (not shown in FIG. 1). The plane defect includes an interstitial stacking fault ((g) in FIG. 1), a vacancy-type stacking fault ((g) in FIG. 1), a twin (not shown in FIG. 1) and a grain boundary (not shown in FIG. 1). And, the volume defect includes a precipitate ((i) in FIG. 1) and a void ((j) in FIG. 1).
Meanwhile, these crystal defects range from atomic level to molecular level, and their crystallographic structures are difficult to recognize and detect. And, considering impurities not caused by crystal growing, it is more difficult to recognize and detect defects or impurities on or in a wafer. Further, new defects or impurities are discovered and named according to physical and chemical characteristics of their crystallographic structures and development of detection systems. According to this criteria, defects can be classified as shown in Table 1.
TABLE 1Vacancy-type defectInterstitial-type defectDetectionVolumePlanePointPointPlaneVolumetechniquedefectdefectdefectdefectdefectdefectReferenceEtching,COPLDPVisible rayFPDEPDSEPDSEPDLSTDHeating,P-bandB-bandEtching,(OiSF)Visible rayHeating,V-clusterP-bandPVPIB-bandI-clusterMetal impuritiesElectricalmeasurementHandAir pocketCOP: Crystal Originated ParticleFPD: Flow Pattern DefectSEPD: Secco Etch Pit DefectLSTD: Laser Scattering Tomography DefectLDP: Large Dislocation PitEPD: Etch Pit Dislocation
And, newly discovered defects are generally detected when a completed wafer is inspected or a semiconductor device is formed on a wafer and inspected. In particular, as a wafer moves toward larger diameter and a required quality level becomes higher, defects that were not regarded as a problem or detected in the past are regarded as a problem or discovered. If such defects have not been reported so far, they are named and reported through extremely difficult study and analysis of their cause and generation mechanism.